This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-190696, filed Jun. 26, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to a substrate cleaning method and substrate cleaning apparatus for performing a cleaning process including a drying process by use of liquid agents and pure water.
A semiconductor device such as an IC and LSI is formed by performing a design step of designing an integrated circuit to be formed on a semiconductor substrate, a mask forming step of drawing a mask pattern used for forming the integrated circuit by use of an electron beam, a wafer forming step of forming a wafer with a preset thickness from a semiconductor single crystal ingot of silicon, for example, a wafer processing step of forming semiconductor elements of the integrated circuits and the like on the wafer, an assembling step of dividing the wafer into semiconductor chips and respectively packaging them to form semiconductor devices, and a test step.
The wafer processing step includes a plurality of steps and a cleaning step is further added thereto to remove dust such as organic-series impurities attached while the steps are effected. Since the dust attached to the surface of the wafer may cause the manufactured semiconductor device to become defective, much effort has been made in order to eliminate the dust. The cause for making the formed semiconductor device defective by the dust attached to the surface of the wafer will not occur only in the case of the semiconductor device. For example, the same cause occurs in a case wherein a liquid crystal display device is formed or a photo-mask used for forming the semiconductor device or liquid crystal display device is formed, and therefore, much effort has been made to eliminate dust in the process for manufacturing the liquid crystal display device or the photo-mask.
Conventionally, in the manufacturing process of the semiconductor device, the semiconductor substrate of silicon or the like is cleaned and polished by use of not only deionized water (pure water) and ultra-pure water but also electrolyzed water obtained by electrolyzing the pure water or ultra-pure water. So far, a fluorine-series solvent has been used for cleaning the semiconductor substrate and the like, but since the solvent gives a bad influence on the living environments, it becomes out of favor and water such as pure water and ultra-pure water is utilized as the most safe solvent.
The pure water is water with high purity from which impurities such as ions, fine particles, micro-organism and organic material are almost completely removed and whose resistivity is approximately 5 to 18 Mxcexa9cm. The ultra-pure water is water which has extremely high purity higher than the pure water and from which suspension (suspended substances) and dissolved substances are removed with high efficiency by use of a ultra-pure water forming device.
Conventionally, the cleaning process for the wafer or the like is effected as follows. The wafer is rotated with the rear surface of the wafer held by a vacuum suction type spin chuck. Then, a cleaning liquid such as pure water is dropped from a nozzle onto a rotating roll-like brush and the wafer surface is cleaned by bringing the brush into contact with the wafer.
Conventionally, an acid liquid agent was continuously emitted onto a to-be-cleaned substrate in order to eliminate the organic-series impurity, then the acid liquid agent on the to-be-cleaned substrate was washed out by use of pure water and the to-be-cleaned substrate was dried. The liquid agent was washed out before drying by spinning the substrate at a high speed, but the temperature of the pure water used at this time was set at a room temperature. Further, when the to-be-cleaned substrate was spin-dried, the number of setting values of the rotating speed was only one. If a heating mechanism for the pure water or liquid agent was provided, the pressure in the pipe between the heating mechanism and the emission port (nozzle) of the cleaning chamber was not taken into consideration.
Thus, the conventional organic-series impurity removing process by use of the acid liquid agent exhibited an extremely high cleaning effect, but there was a possibility that the acid liquid agent adhered to the to-be-cleaned substrate. Further, the cleaning process by use of the acid liquid agent utilized the high reactivity thereof, and in this case, there occurred a possibility that splash of the liquid agent occurred to contaminate the inner wall of the cleaning chamber (cup) and the contaminant would fall on the to-be-cleaned substrate at the time of drying by high speed rotation.
Further, if the liquid agent is washed out by use of pure water of the room temperature, the pure water remains at the center of the surface of the to-be-cleaned substrate to the last when the drying process utilizing centrifugal force caused by the high speed rotation is effected. If the pure water of the room temperature runs on the to-be-cleaned substrate at high speed, static electricity occurs due to friction between the pure water and the substrate surface, and there occurs a possibility that a pattern formed on the to-be-cleaned substrate is destroyed when charges are discharged.
If the cleaning liquid is set at a high temperature, the viscosity of the cleaning liquid becomes low, and friction between the inner wall of the pipe and the cleaning liquid becomes small. Leakage of the cleaning liquid from the nozzle will occur for a while after interruption of emission of the liquid agent or the like due to a reduction in the friction between the inner wall of the pipe and the cleaning liquid. Particularly, if pure water is kept leaked for a while when the substrate is spin-dried after washing-out by pure water, the leaked pure water will drop on the to-be-cleaned substrate.
This invention has been made to solve the above problem and an object of this invention is to provide a substrate cleaning method for efficiently removing an acid liquid agent remaining on a to-be-cleaned substrate after cleaning in the method for cleaning the to-be-cleaned substrate by use of an acid liquid agent and a substrate cleaning apparatus used in the above substrate cleaning method.
In order to attain the above object, a substrate cleaning method according to a first aspect of this invention comprises cleaning a to-be-cleaned substrate disposed in a cleaning cup by use of an acid liquid agent; and cleaning the substrate by use of an alkaline liquid agent in the cleaning cup to neutralize residue of the acid liquid agent after the step of cleaning by use of the acid liquid agent.
A substrate cleaning method according to a second aspect of this invention comprises oxidizing impurities on the surface of a to-be-cleaned substrate by use of an oxidizing agent; and cleaning the to-be-cleaned substrate by use of a reducing agent to remove the oxidized impurities after the oxidizing step.
A substrate cleaning apparatus according to a third aspect of this invention comprises a cleaning cup configured to receive a to-be-cleaned substrate; a table disposed in the cleaning cup, configured to support the to-be-cleaned substrate; a first nozzle disposed in the cleaning cup, configured to supply an acid liquid agent; a second nozzle disposed in the cleaning cup, configured to supply an alkaline liquid agent; a third nozzle disposed in the cleaning cup, configured to supply hot pure water; a pure water heating mechanism configured to supply the hot pure water; a branch line formed in an intermediate portion of a pipe extending from the pure water heating mechanism to the third nozzle configured to supply the hot pure water to lower water pressure in the pipe; and a control mechanism configured to control the operations of the first to the third nozzle and the pure water heating mechanism.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.